Product Guide

22mm Industrial Alarms with LED Lights (Product Application Guide)


  • 16 Volt units are DC Only; 28 Volt units can be DC or AC/DC; 120 Volt units are AC Only
  • Multi-tone units are 28 Vdc Only

Sound Types

  • Continuous Tone: Constant tone until voltage is removed
  • Fast Pulse Tone: 10 pulses per second
  • Medium Pulse Tone: 5 pulses per second
  • Slow Pulse Tone: 1 pulse per second
  • Fast Double Pulse Tone: 1 double beep every half second
  • Slow Double Pulse Tone: 1 double beep every 2 seconds
  • Short Pulse Tone: 1 beep per second (on for 0.1 sec / off for 0.9 sec)
  • 10 Sec. Delay: Wait 10 seconds before issuing continuous tone
  • Fast Speed-Up: Over 30 sec’s, speed up from 1 beep per 2 sec’s to 8 beeps per sec
  • Chime Tone: Repeating chime sound at 1 chime every 3 seconds (Slow Chime) or 1 chime per second (Fast Chime)
  • Fast Warble: Alternate between two frequencies at 7 warbles per second
  • Slow Warble: Alternate between two frequencies at 1.5 warbles per second
  • Fast Siren: Sweeping siren sound at 5 sweeps per second
  • Slow Siren: Sweeping siren sound at 2 sweeps per second

Multi-Tone Descriptions:

  • MT1: Continuous; Slow Pulse; Fast Pulse, Chirp
  • MT2: Continuous; Slow Pulse; Fast Pulse, Slow Chime
  • MT3: Continuous, Slow Pulse, Fast Pulse, Fast Chime
  • MT4: Continuous, Slow Pulse, Fast Pulse, Slow Warble
  • MT5: Continuous, Slow Pulse, Fast Pulse, Fast Warble
  • MT6: Continuous, Slow Pulse, Fast Pulse, Fast Siren
  • MT7: Continuous, Slow Pulse, Fast Pulse, Slow Siren
  • MT8: Continuous, Fast Pulse, Slow Chime, Slow Warble

Mounting Instructions:

  • Panel Hole Size:5 mm with Keyway
  • Maximum Panel Thickness:7 mm (0.5 in)
  • Maximum Nut Torque: 10 in-lbs (1.13 n-m)

Electrical Connection:



  • Wire Strip Length:5 mm (0.256 in)
  • Wire Size: 30 to 16 AWG
  • Maximum Screw Torque: 2 in-lbs (0.226 n-m)

Sound Level vs Distance:

ZT Series Sound Level Category

85 – 95 dB @ 2 ft
75 – 85 dB @ 2 ft
65 – 85 dB @ 2 ft
10 cm (4 in)100 to 110 dB90 to 100 dB80 to 90 dB
30 cm (1 ft)91 to 101 dB81 to 91 dB71 to 81 dB
1 Meter82 to 92 dB72 to 82 dB62 to 72 dB
10 ft71 to 81 dB61 to 71 dB51 to 61dB

  • The ZT Series of 22mm alarms measures sound level at 2 feet. Since sound level drops over distance, the above chart lists the equivalent sound levels at various distances.
  • For example, if the Mallory part is in the LOUD sound level category, it has a sound level of 85 to 95 dB at 2 feet. At 10 cm, the sound level would measure 100 to 110 dB.


  • Standard orders are bulk packed.

Accessories & Replacement Parts:

Part NumberDescriptionNotes
22MMGASKETReplacement NEMA GasketGasket comes with part
22MMNUTReplacement NutNut comes with part

UL On-Line Card

cUL On-Line Card

Piezoelectric Electronic Alarm Construction

The above cross section picture shows the basic elements used in a piezoelectric audible alarm.  The area in front of the transducer element including the front hole opening forms an acoustic cavity that lets the sound radiate out with the most efficiency (i.e. loudest sound level).  If the alarm is an indicator that contains a circuit board, the circuit board is attached to the piezoelectric sounder element via soldered wires.

The above picture can be interpreted to represent a board mount package with pc pin terminations, but the same concept is used when building audible alarms in other mounting configurations such as SMT, Flange Mount, and Panel Mount alarms.

If the back of the alarm is sealed with epoxy or other material, the “guts” of the alarm (including the circuit board and components) are protected against fluid intrusion.  However, fluid sitting inside the front cavity can obstruct the operation of the device causing the sound level to decrease significantly.  If you need to wash the alarms after a soldering operation, it is strongly recommended to use an alarm that comes with a wash label that keeps the washing fluid from getting inside of the front cavity.

Operation of Piezoelectric Audible Alarms

Piezoelectric electronic audible alarms work by converting the user input voltage to an appropriate oscillating signal that is applied to a sounder element that is mounted in a housing.  The piezoelectric sounder element consists of a metal disc that has a special ceramic material bonded to it that physically bends when voltage is applied to it.

The above picture shows a bare piezoelectric sounder element.  By applying a sinusoidal wave-form at an appropriate frequency, the transducer will physically deflect in one direction and then in the opposite direction following the shape of the input wave-form.  If this oscillation occurs in the audible frequency range (1 Hz to 20 kHz), then air pressure waves are produced that the human ear interprets as an audible sound.

The larger the voltage of the applied wave-form, the larger the amplitude of the air pressure waves resulting in a louder sound level.  However, the ceramic portion of the transducer can only bend so far before there is a risk of a catastrophic failure.  This maximum voltage is somewhere around 40 to 50 volts.  However, it is rare to apply this much voltage to a transducer as you reach a point of diminishing returns for voltages much greater than 32 volts.

By itself, the sound level produced by a transducer element is insignificant.  To increase the size of the air pressure waves (and thus the sound level), the transducer element must be mounted inside an acoustic chamber that is optimized for the transducer size and resonant frequency.  Every transducer has one frequency where it flexes more efficiently producing the louder sound levels.  This frequency where the transducer performs the best is called the resonant frequency.

Self-Drive type devices provide a 3rd terminal that connects to an isolated portion of the piezoelectric transducer.  This third terminal provides a feed-back signal that is 180 degrees out of phase with the drive signal.  This signal can be fed back into the circuit to allow the sounder element to self-tune itself to the transducer’s resonant frequency.

Decibel Sound Level Scale

The decibel sound level scale is an arbitrary scale that ranges from 0 dB (threshold of hearing) to 130 dB (threshold of pain).  The chart below shows where some common sounds fall on this dB scale.  Audible alarms are available that have sound levels as soft as 55 dB at 2 feet and as loud as 110 dB at 2 feet.

Fundamental Frequency & Harmonics

Below is a frequency scan of a piezoelectric audible alarm that has a resonant frequency of 2,800 Hz.  As you can see, there is a strong frequency peak at 2.8 kHz and several smaller frequency peaks that follow called harmonic frequencies.  The table below the chart shows that the size of the harmonic frequencies are significantly smaller than the fundamental frequency for this particular alarm unit.  Because this alarm has a large fundamental frequency and much smaller harmonic frequencies, the sound quality of this part will be very good.  When this alarm is activated, the listener will hear one clear frequency (also called sound pitch) from the alarm.  Other electronic alarm technologies such as electro-magnetic or electro-mechanical type alarms often have much larger harmonic frequency components resulting in less clear tone.

Typical Failure Modes of Piezoelectric Audible Alarms

Component/SubsystemFailure ModeEnd ResultOccurrence
Circuit Components (Resistors, Capacitors, Diodes, IC’s, etc.)Over-voltage by customer’s applicationUnit ceases working.Vast Majority of Returns
Transducer/Wire Solder OperationNot enough wire strands in solder jointWire breaks after period of time & unit ceases soundingRare
Physical AssemblyTransducer wire pinched, adhesive/epoxy run down onto transducer, or RTV adhesive seal failureIntermittent operationRare
Soldering OperationIncorrect Solder Temperature or Time Causing Cold Solder JointIntermittent operation or unit ceases working after period of timeVery Rare
Circuit ComponentsRandom Component Failure; Wrong Component Used; Missing ComponentUnit ceases working under normal operating conditionsVery Rare
Transducer WireDefect in Wire; Wire Strands Damaged in ProductionWire breaks after period of time & unit ceases soundingVery Rare
Piezo TransducerIncorrect Polarization by Manufacturer; Glue Bonding FailureSound volume level decreases over time.Exceedingly Rare


  1. Customer returns of Mallory audible alarms for failure to operate are very rare. Of the few parts returned each year, the vast majority of the root cause of failure is an over-voltage or voltage spike condition caused by the customer’s application.
  2. All Mallory alarms are, at a minimum, function tested 100% during production, and a final audit is performed. Mallory SC/SBM/SBT/SBS/SNP/LSC/VSB/MSR/MSO/ZA series of alarms are audited 100% at final test by checking that sound level, frequency, and current are within specification limits from 2 to 4 different voltage levels.

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